US4590615A - Multipath distortion reducing circuit - Google Patents

Multipath distortion reducing circuit Download PDF

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Publication number
US4590615A
US4590615A US06/622,336 US62233684A US4590615A US 4590615 A US4590615 A US 4590615A US 62233684 A US62233684 A US 62233684A US 4590615 A US4590615 A US 4590615A
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Prior art keywords
output
signal
detecting means
detecting
coupled
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Expired - Fee Related
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US06/622,336
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English (en)
Inventor
Kiyoshi Ohtaki
Kohji Ishida
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Pioneer Corp
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Pioneer Electronic Corp
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Assigned to PIONEER ELECTRONIC CORPORATION reassignment PIONEER ELECTRONIC CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: ISHIDA, KOHJI, OHTAKI, KIYOSHI
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H04B1/1646—Circuits adapted for the reception of stereophonic signals
    • H04B1/1661—Reduction of noise by manipulation of the baseband composite stereophonic signal or the decoded left and right channels
    • H04B1/1669—Reduction of noise by manipulation of the baseband composite stereophonic signal or the decoded left and right channels of the demodulated composite stereo signal
    • H04B1/1676—Reduction of noise by manipulation of the baseband composite stereophonic signal or the decoded left and right channels of the demodulated composite stereo signal of the sum or difference signal

Definitions

  • the present invention relates to a circuit for reducing the amount of multipath distortion in an FM tuner.
  • FIG. 1 An example of a conventional multipath distortion reducing circuit of this type is shown in FIG. 1.
  • the output terminal of a front end 1 is connected to a 10.7 MHz bandpass filter (BPF) 2, the output terminal of which is connected to the input terminal of an FM detector 3.
  • BPF bandpass filter
  • the output terminal of the FM detector 3 is connected to the input terminal of a stereo demodulator 4.
  • the latter provides a left channel output and a right channel output respectively at a left channel output terminal 5 and a right channel output terminal 6.
  • a series circuit of a capacitor C and a switch SW is connected between the output terminals 5 and 6.
  • the switch SW connected between the left channel output terminal 5 and the right channel output terminal 6 is turned on.
  • high-frequency noise components contained in the right and left channel outputs which are offensive to the ear and which are opposite in phase to one another, are cancelled out, being shorted by the capacitor C.
  • the perceived noise level is reduced.
  • the circuit is disadvantageous in that, the higher the frequency of the cancelled-out signal components, the larger the ratio of mixing of right and left channels, and the lesser the degree of separation between the two channels.
  • An object of this invention is to eliminate the above-described difficulties accompanying a conventional multipath distortion decreasing circuit.
  • the invention provides a circuit in which the envelope of the IF signal is detected to form a distortion cancelling signal which is applied to reduce the amount of multipath distortion.
  • FIG. 1 is a block diagram showing an example of a conventional multipath distortion reducing circuit
  • FIG. 2 is a block diagram showing an example of a multipath distortion reducing circuit according to the invention.
  • FIG. 3 is a graphical representation indicating the characteristic of a differentiator in FIG. 2;
  • FIGS. 4A-4E are diagrams showing waveforms at various circuit points in the circuit of FIG. 2;
  • FIG. 5 is a graphical representation showing a multipath distortion characteristic obtained by calculation
  • FIG. 6 is a graphical representation showing a characteristic obtained by multiplication of the outputs of an AM detector and of the differentiator shown in FIG. 2;
  • FIG. 7 is a block diagram showing another example of a circuit according to the invention.
  • the output terminal of a front end is connected to a first 10.7 MHz BPF 2 and a second 10.7 MHz BPF 7.
  • the output terminal of the first 10.7 MHz BPF 2 is connected to an FM detector 3, the output terminal of which is connected to a differentiator 10 and one input terminal of an adder 12.
  • the output terminal of the second 10.7 MHz BPF is connected to an input terminal of an AM detector 8.
  • the output of the AM detector 8 is utilized to apply automatic gain control (AGC) to the AM detector 8 with the aid of an AGC circuit 9.
  • AGC automatic gain control
  • the output terminal of the differentiator 10 is connected to one input terminal of a multiplier 11, the other input terminal of which is connected to the output terminal of the AM detector 8.
  • the output terminal of the multiplier 11 is connected to the other input terminal of the adder 12, the output terminal of which is connected to a stereo demodulator 4.
  • the stereo demodulator 4 provides a left channel output and a right channel output, respectively, at a left channel output channel 5 and a right channel output terminal 6.
  • the output of the FM detector 3 is as shown in FIG. 4A and an IF signal outputted by the front end 1 is as shown in FIG. 4B. It can be understood that a certain relation exists between the signals shown in FIGS. 4A and 4B. In accordance with the invention, this relation is utilized to reduce the amount of multipath distortion.
  • the envelope of the output of the front end 1 (shown in FIG. 4B) is detected to form a distortion cancelling signal.
  • the multipath distortion is decreased by subtracting the distortion cancelling signal thus formed from the FM detection output.
  • the output of the front end 1 is applied to the second 10.7 MHz BPF, which has a flat in-band amplitude characteristic, to remove unwanted interference components therefrom.
  • the output thus treated is applied to the AM detector 8 under automatic gain control to detect the envelope of the IF signal.
  • the envelope signal as shown in FIG. 4C, has a constant amplitude irrespective of the presence or content of the IF signal due to the automatic gain control effect applied thereto.
  • the differentiator 10 and the multiplier 11 are provided as shown in FIG. 2.
  • the differentiator 10 has a gain-phase characteristic as shown in FIG. 3.
  • the output of the FM detector 3 is shifted by 90° in phase when applied to the differentiator 10 to convert it to a waveform as shown in FIG. 4D.
  • This signal and the signal shown in FIG. 4C are subjected to multiplication by the multiplier 11 to obtain the cancelling signal shown in FIG. 4E.
  • the cancelling signal is applied to the adder 12 where it is subtracted from the detection output shown in FIG. 4A. As a result, a signal in which the multipath distortion has been substantially reduced is provided at the output terminal of the adder 12.
  • FIG. 5 is a graphical representation showing the multipath distortion characteristic described by the above expression in which the horizontal axis represents time and the vertical axis represents the magnitude of the multipath distortion.
  • FIG. 6 A characteristic plotted according to this expression is as shown in FIG. 6. As is apparent from a comparison of FIGS. 5 and 6, the characteristic of FIG. 6 is similar to that of FIG. 5. Thus, the reduction in the amount of multipath distortion brought about with the use of the invention has been proven.
  • the differentiator 10 receives the output of the FM detector 3. However, it may receive the output of the adder 12 as shown in FIG. 7.
  • the mulipath distortion reducing circuit according to the invention is so designed that a multipath distortion cancelling signal is formed by detecting the envelope of the IF signal, thereby to decrease the multipath distortion. Therefore, with the circuit of the invention, the amount of multipath distortion can be decreased without lowering the degree of separation.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Noise Elimination (AREA)
US06/622,336 1983-07-06 1984-06-19 Multipath distortion reducing circuit Expired - Fee Related US4590615A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP58122505A JPS6014524A (ja) 1983-07-06 1983-07-06 マルチパス歪低減回路
JP58-122505 1983-07-06

Publications (1)

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US4590615A true US4590615A (en) 1986-05-20

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Family Applications (1)

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US06/622,336 Expired - Fee Related US4590615A (en) 1983-07-06 1984-06-19 Multipath distortion reducing circuit

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US (1) US4590615A (ja)
JP (1) JPS6014524A (ja)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4726073A (en) * 1985-10-02 1988-02-16 U.S. Philips Corporation Receiver including a multipath transmission detector
US5249233A (en) * 1992-04-06 1993-09-28 Ford Motor Company Multipath noise minimizer for radio receiver
US5408685A (en) * 1992-04-06 1995-04-18 Ford Motor Company Multipath detector using phase comparison of stereo pilot signal
WO1995034140A1 (en) * 1994-06-03 1995-12-14 Motorola, Inc. Method and apparatus for cancelling interference in signals having undergone multipath
US5554955A (en) * 1995-08-28 1996-09-10 Myers; Glen A. Method and apparatus for removing the effects of co-channel interference from the message on a dominant frequency modulated carrier and for recovering the message from each of two co-channel carriers
US5828954A (en) * 1996-04-04 1998-10-27 Lucent Technologies Inc. Transmission system for digital audio broadcasting
EP1158692A2 (en) * 2000-05-24 2001-11-28 NTT DoCoMo, Inc. Method for multipath detection in wireless communication apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6216621A (ja) * 1985-07-16 1987-01-24 Clarion Co Ltd Ｆｍ受信回路

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3176231A (en) * 1961-03-21 1965-03-30 Itt System for cancellation of ground reflections
US4166251A (en) * 1977-05-30 1979-08-28 Victor Company Of Japan, Ltd. System for removing interference distortion in the demodulated signal of a frequency-modulated signal
US4266296A (en) * 1978-11-16 1981-05-05 Victor Company Of Japan, Limited Multipath distortion compensation circuit and method
JPS57125542A (en) * 1981-01-29 1982-08-04 Nissan Motor Co Ltd Multi-path distortion detector for fm radio receiver

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3176231A (en) * 1961-03-21 1965-03-30 Itt System for cancellation of ground reflections
US4166251A (en) * 1977-05-30 1979-08-28 Victor Company Of Japan, Ltd. System for removing interference distortion in the demodulated signal of a frequency-modulated signal
US4266296A (en) * 1978-11-16 1981-05-05 Victor Company Of Japan, Limited Multipath distortion compensation circuit and method
JPS57125542A (en) * 1981-01-29 1982-08-04 Nissan Motor Co Ltd Multi-path distortion detector for fm radio receiver

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
Ishigaki et al.; "Electronic Reduction of FM Distortion Caused by Multipath Transmission"; I.E.E.E.-Trans. on Consumer Electr.; vol. CE-26, Feb. 1980, pp. 28-35.
Ishigaki et al.; Electronic Reduction of FM Distortion Caused by Multipath Transmission ; I.E.E.E. Trans. on Consumer Electr.; vol. CE 26, Feb. 1980, pp. 28 35. *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4726073A (en) * 1985-10-02 1988-02-16 U.S. Philips Corporation Receiver including a multipath transmission detector
US5249233A (en) * 1992-04-06 1993-09-28 Ford Motor Company Multipath noise minimizer for radio receiver
US5408685A (en) * 1992-04-06 1995-04-18 Ford Motor Company Multipath detector using phase comparison of stereo pilot signal
WO1995034140A1 (en) * 1994-06-03 1995-12-14 Motorola, Inc. Method and apparatus for cancelling interference in signals having undergone multipath
US5554955A (en) * 1995-08-28 1996-09-10 Myers; Glen A. Method and apparatus for removing the effects of co-channel interference from the message on a dominant frequency modulated carrier and for recovering the message from each of two co-channel carriers
US5828954A (en) * 1996-04-04 1998-10-27 Lucent Technologies Inc. Transmission system for digital audio broadcasting
EP1158692A2 (en) * 2000-05-24 2001-11-28 NTT DoCoMo, Inc. Method for multipath detection in wireless communication apparatus
US20020006775A1 (en) * 2000-05-24 2002-01-17 Ntt Docomo, Inc. Wireless communication apparatus and wireless communication method
EP1158692A3 (en) * 2000-05-24 2005-11-30 NTT DoCoMo, Inc. Method for multipath detection in wireless communication apparatus
US7088977B2 (en) 2000-05-24 2006-08-08 Ntt Docomo, Inc. Wireless communication apparatus and wireless communication method

Also Published As

Publication number Publication date
JPS6014524A (ja) 1985-01-25
JPH0354492B2 (ja) 1991-08-20

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